Method of fabricating a surface probing device

ABSTRACT

A method of making a probe having a cantilever and a tip include providing a substrate having a surface and forming a tip extending substantially orthogonally from the surface. The method includes depositing an etch stop layer on the substrate, whereby the etch stop layer protects the tip during process. A silicon nitride layer is then deposited on the etch stop layer. An etch operation is used to release the cantilever and expose the etch stop layer protecting the tip. Preferably, the tip is silicon and the cantilever supporting the tip, preferably via the etch stop layer, is silicon nitride. A probe for a surface analysis instrument made according to the method includes a tip and a silicon nitride cantilever having a thickness defined during the deposition process.

CROSS REFERENCE TO A RELATED APPLICATION

The present application is a divisional of U.S. application Ser. No.10/345,513, filed Jan. 16, 2003, now U.S. Pat. No. 6,886,395.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method of fabricating a surface probingdevice and the probing device produced thereby, and more particularly,to a method of fabricating a silicon tip supported by a silicon nitridecantilever for performing surface analysis on a sample.

2. Description of Related Art

Surface analysis methods have advanced to achieve atomic resolutionusing a probing tip of a surface probing device having an apex of atomicdimensions. The probing tip is usually a tapered silicon structure,often referred to as a stylus, with a base attached to a cantilever armand a sharp apex that interacts with the surface being probed. Moreparticularly, the parts of the surface probing device include a stylus,a cantilever arm and a mounting section. In addition, the surfaceprobing device may have an electrical connection from the stylus,through the cantilever arm, and to external circuitry for monitoringsurface characteristics in a particular mode of operation. Moreover, theprobe device may also have a reflective coating on the cantilever arm toaccommodate, for example, optical detection techniques. In general, theelectrical connection and the reflective coating provide different waysto measure the response of the stylus apex to the surface beinganalyzed.

An apparatus that uses a surface probing device for surface analysistypically involves a scanning process. During the scanning process, thestylus apex responds to surface characteristics. The response ismonitored and generally held constant through a feedback system thatcauses a slight change in the cantilever arm position. Two notableexamples where these general principles apply are scanning tunnelingmicroscopy (STM) and atomic force microscopy (AFM).

In STM, a stylus apex of atomic dimensions on a cantilever arm followsthe contour of a sample surface. Electrons tunnel through a near-fieldvacuum between the conductive apex of the stylus and a conducting samplecreating a tunneling current. The tunneling current is very sensitive tochanges in the distance between the stylus apex and the conductivesample surface. A feedback system is used to monitor and control thetunneling current at a constant value. Optionally, an optical detectiontechniques such as interferometry or laser beam deflection can be usedto measure the resultant cantilever arm deflection during scanning.

AFM uses a stylus that is mounted on a cantilever arm that has a smallspring constant and scans a surface such that repulsive inter-atomicforces between the surface and the stylus apex cause deflections in thecantilever arm position. Again, a feedback system is used to monitor andcontrol the forces between the tip and sample, and an optical detectiontechnique such as interferometry or laser beam deflection are used tomeasure the resultant cantilever arm deflection during the scanningprocess. In AFM, different modes of operation may be employed. See, forexample, U.S. Pat. No. 6,189,374, filed Mar. 29, 1999, assigned to thepresent assignee, and entitled Active Probe For An Atomic ForceMicroscope And Method Of Use Thereof.

Several methods for fabricating surface probing devices with a stylusand a cantilever arm have been reported. Bothra et al., U.S. Pat. No.5,540,958, describe a method for making a stylus on a cantilever arm byfirst etching a silicon wafer with a mask to produce protruding shapesof a predetermined size and then depositing a second layer, such assilicon oxide, by electron cyclotron resonance. Shimada et al., in U.S.Pat. No. 5,546,375 describe making a stylus by forming a recessed cavityin a silicon wafer. The cavity is then used to define the structure ofthe stylus. In U.S. Pat. No. 5,399,232, Albrecht et al. describe amethod of fabricating a cantilever arm and stylus again by forming adepressed area in a silicon wafer and using the depressed area to definethe stylus shape. In U.S. Pat. No. 5,581,083, Majumdar et al. describe amethod for producing a hole at the apex of a stylus. The method uses avoltage applied to a metal coated tip causing evaporation of the metalcoating and exposing the underlying silicon apex. Manalis et al., inU.S. Pat. No. 6,156,216, describe a silicon nitride cantilever with asilicon tip but provide no way for making a tip useable for probemicroscopy, nor a means to control the characteristics of the silicontip while removing the silicon nitride covering.

As noted, the combination of a stylus and a cantilever arm is importantfor many modern surface probing methods. In addition, each method ofanalysis typically requires a stylus and a cantilever arm withproperties tailored to the application at hand. A significant drawbackin this regard is that known methods to fabricate silicon stylusessupported by cantilever arms include making the cantilever arms fromsilicon using an etching process. One difficulty that can arise infabricating surface probing devices with silicon cantilever arms is thatthe thickness of silicon is difficult to control by etching. Anotherdrawback is that it is beneficial for some applications such as thermalmeasurement and electrical measurement to make surface probing devicesthat contain an electrically isolated stylus which can be connected toexternal circuitry through a conductive metal deposited on thecantilever arm.

Therefore, the field of fabricating such surface probing device is inneed of a method for fabricating corresponding styluses and cantileverarms in which the thickness of the cantilever arm is easy to controlduring the fabrication process and which yields an electrically isolatedsilicon tip. Moreover, it is important that the stylus be extremelysharp or, alternatively, small. A typical state of the art silicon AFMprobe tip has a radius of curvature smaller than 15 nm. However,cantilevers with lower spring constants, such as silicon nitridecantilevers typically have styluses with radii of curvature greater than25 nm. This is due to the fact that silicon nitride tips are typicallymolded, thus yielding tips that are necessarily less sharp. Contrary tosuch silicon nitride tips, silicon tips can be readily sharpened via anoxidation step. Therefore, in applications that require the low forceafforded by the silicon nitride cantilever, resolution due to stylussize must be sacrificed.

In sum, a method that workably combines a silicon tip with a siliconnitride cantilever is thus desired to achieve the benefits of bothsystems, i.e., a low force silicon nitride cantilever and a sharpsilicon tip.

SUMMARY OF THE INVENTION

The preferred embodiment overcomes the drawbacks of known methods byproviding a method of fabricating a probing device having a cantileverarm that is composed of silicon nitride and which is useful as a lowforce cantilever sensor. Moreover, the resultant probing device (i.e.,probe) has a silicon tip which, in addition to being made of silicon,has a very sharp stylus apex.

According to one aspect of the preferred embodiment, a method of makinga probe having a cantilever and a tip includes providing a substratehaving a surface and forming a tip extending substantially orthogonallyfrom the surface. The method includes depositing an etch stop layer onthe substrate, whereby the etch stop layer protects the tip duringprocess. A silicon nitride layer is then deposited on the etch stoplayer. An etch operation is used to release the cantilever and exposethe etch stop layer protecting the tip. Preferably, the tip is siliconand the cantilever is silicon nitride and supports the tip, preferablyvia the etch stop layer.

In another aspect of the preferred embodiment, a method of making aprobe includes the steps of providing a wafer and forming a stylus ofpredetermined width and height on a top surface of the wafer. The methodincludes sharpening and protecting the stylus with silicon dioxidewhich, as a result, creates a silicon dixode layer. A silicon nitride isthen deposited so as to have a defined thickness, and the stylus isrevealed using an etch mask and a subsequent etch, wherein the etch isterminated on the silicon dioxide layer.

According to a further aspect of the preferred embodiment, a method offabricating a scanning probe device includes forming a cantilever by adeposition process, and integrating a metal tip with the cantilever.

According to yet another aspect of the preferred embodiment, a method offabricating a scanning probe device comprises forming a cantileverincluding depositing a layer of a material and then integrating athermocouple with the cantilever after the depositing step.

In a further aspect of the preferred embodiment, a method of fabricatinga scanning probe device includes forming a layer of material andintegrating an optical element with the layer, wherein the opticalelement is accessible from a side opposite a side on which the opticalelement was integrated with the layer.

In a still further aspect of the preferred embodiment, a method ofproducing a probe includes forming a cantilever comprising a layer of afirst material having a thickness defined by the deposition process, andforming a tip of a second material. In this case, the first and secondmaterials are different, and the tip and the cantilever are coupled. Thefirst material is preferably silicon nitride, while the second materialmay constitute the substrate material, such as the silicon of a siliconwafer. Alternatively, the second material could be a metal.

Another feature of the preferred embodiment includes a probe having asilicon tip and a silicon nitride cantilever. The tip is supported bythe cantilever via an oxide layer.

According to another aspect of the preferred embodiment, a probe for asurface analysis instrument includes a tip and a silicon nitridecantilever. The silicon nitride cantilever is formed using a depositionprocess.

In another aspect of this embodiment, the tip is silicon and isoxidation sharpened. Moreover, the tip preferably includes a reflectiveelement disposed on the cantilever that includes a front side and a backside. Notably, the reflective element may be disposed on the front side.

In the preferred embodiment, a method for making surface-probing devicescan be used to produce devices whereby the silicon material isrestricted to the stylus and mounting sections, and the cantilever armsare silicon nitride. An advantage of this method is that the siliconnitride layer is formed by a deposition process rather than by anetching process, thus allowing for better control of the cantilever armthickness over silicon arms that must be produced using an etchingprocess. Importantly, the preferred method provides flexibility in thefabrication of silicon nitride cantilever arms so that correspondingspring constants can be engineered for specific applications.Additionally, by providing an electrically isolated silicon stylus, theprobing device is particularly useful, for example, where small currentsare being measured.

In process, a silicon stylus is formed on the top working surface of thewafer by etching the wafer. Once the stylus has been formed, the stylusor the apex of the stylus can be ion implanted to alter the chemicalcomposition. To ensure that the silicon stylus is sharp, the siliconwill be oxidation sharpened according to known techniques prior to thedeposition of the silicon nitride layer. This oxide layer will alsoserve as an etch stop when etching the subsequently deposited siliconnitride layer. This etch stop will prevent damage to the silicon stylusduring the silicon nitride removal and ensure the requisite sharpstylus. Notably, this oxide layer can also be used as protection duringthe final cantilever release. This can be quite important because therelease process will likely damage the stylus if it is not protected.Using the integrated etch stop is a far better alternative over tryingto protect the tip with an additional process step. Using the originalpassivation will never expose the fragile tip until all processing iscomplete, and this will result in a higher quality tip and better yield.

A silicon nitride layer is then deposited over the silicon dioxidecovered silicon stylus and top working surface of the wafer. At thispoint, an optional reflective metal coating can be applied andoptionally patterned on the front side of the wafer. A protective etchmask is applied on the silicon nitride layer, including over the siliconnitride covered silicon stylus. The properties of the resist and itsapplication are engineered to deposit a thickness of resist less thanthe height of silicon stylus. The process of controlling depositionthickness is well known to those familiar in the art.

The silicon nitride covered silicon stylus is then etched to expose adesired underlying portion of the silicon dioxide covered silicon stylusapex. The etch will consume some of the protective resist, so if thereis slight coverage of the apex this will be removed and it will notinterfere with the process. This process can be repeated multiple timesin order to fully “clear” the stylus apex without damaging the wafersurface silicon nitride. Notably, in the final iteration of the resistapplication, the cantilever can also be lithographically defined.

A silicon stylus supported on a silicon nitride cantilever arm is thenmade by etching the bottom surface of the wafer away in the region wherethe cantilever is desired. The etch is stopped when the field silicon iscompletely consumed and only the stylus silicon remains. The protectiveoxide layer is then removed in an etch that is highly selective tosilicon nitride and silicon.

A reflective coating can then optionally be applied to the back side ofthe cantilever to facilitate optical detection techniques. Note that thereflective coating can optionally be applied, in process, on the frontside of the cantilever as highlighted previously.

In another embodiment, a metal stylus supported by a silicon nitridecantilever can be formed by following the above process through theetching of the bottom surface of the cantilever. In this embodiment thebottom surface is fully etched, including the stylus. Since the stylusis completely etched, application of the silicon dioxide layer isoptional. If the silicon dioxide layer is used, the silicon dioxideprotective layer is then removed, typically using an appropriate etch.Metal is then deposited from the back side of the device. As metal isdeposited on, and through, the silicon nitride aperture, the aperturecloses. The result of the deposition will be the formation of a metaltip with electrical contact to the base of the cantilever.

By subsequently depositing a different metal onto the front side of thesilicon nitride cantilever with metal stylus, a thermally sensitivestylus can be formed. It is well known that dissimilar metals in contactwill produce a voltage that is proportional to temperature. In thisconfiguration, the dissimilar metals touch only at the apex. Contact ismade to each metal from the front and back sides of the cantilevermounting section, respectively.

These and other objects, features, and advantages of the invention willbecome apparent to those skilled in the art from the following detaileddescription and the accompanying drawings. It should be understood,however, that the detailed description and specific examples, whileindicating preferred embodiments of the present invention, are given byway of illustration and not of limitation. Many changes andmodifications may be made within the scope of the present inventionwithout departing from the spirit thereof, and the invention includesall such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred exemplary embodiment of the invention is illustrated in theaccompanying drawings in which like reference numerals represent likeparts throughout, and in which:

FIGS. 1A-D are side elevational views of a probe device being producedaccording to a preferred embodiment, including showing the steps formaking a silicon nitride layer with a protruding silicon stylus and backside reflective coating;

FIGS. 2A-D are side elevational views of a probe device of a preferredembodiment, including showing the steps for making a silicon nitridelayer with a protruding silicon stylus and frontside reflective coating;

FIGS. 3A-D are side elevational views of a probe device of a preferredembodiment, including showing the steps for making a silicon nitridelayer with a protruding metal stylus;

FIGS. 4A and 4B are side elevational views of a probe device accordingto a preferred embodiment, including showing the steps for making asilicon nitride layer with a protruding thermally sensitive stylus; and

FIG. 5 is a flow diagram illustrating a method of producing a siliconnitride probe according to a preferred embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment is directed to etching the top working surfaceof a wafer to form a silicon stylus with a predetermined geometry. Hereand throughout the descriptions, working surfaces refer to the surfacesof interest that a specified operation is being performed on. For easeof presentation, “top” refers to the working surfaces of the wafer thatare part of the silicon stylus formed or to be formed, while “bottom”refers to working surfaces that are not part of the silicon stylus to beformed or formed. The wafer is typically either a silicon wafer, ap-doped silicon wafer, an n-doped silicon wafer, a p-dopedsilicon-on-insulator (SOI) wafer or a n-doped silicon-on-insulatorwafer.

FIGS. 1A-1D show steps for making a silicon nitride layer with aprotruding silicon stylus. A wafer 50 is provided with a top siliconworking surface 52 and a bottom silicon working surface 54. The wafer 50is a silicon wafer or a silicon-on-insulator wafer. In the case shown,the wafer is a silicon wafer that is p-doped, n-doped or un-dopedsilicon. The top working surface 52, as shown in FIG. 1A, has beenetched, according to known techniques, the details of which are readilyavailable to produce a silicon stylus 60 with a height from 0.1 μm to 50μm, but typically about 10 μm. The silicon stylus 60 is a taperedsilicon structure that has an apex 62 and a base 64, as shown in FIG.1A.

Note that the silicon stylus 60 can be doped at any time during themethod described when the silicon stylus or stylus apex is exposed. Thepreferred method for doping the stylus is by ion implantation, but anyknown method may be employed. Notably, doping is useful for altering theconductivity of the tip itself. There are many reasons to control theconductivity including reducing electrostatic effects during dynamicoperation, and having the ability to use the tip as an electrical ohmicpoint probe or an electric field probe. When using the tip 60 in suchelectrical applications, a metal element (not shown) may be connectedfrom the tip 60 to the die or probe mount (not shown) in order tofacilitate connection to the instrument. Doping may also be changed inorder to use the high doping as an etch stop, for example, in order tomake a “shell” tip. It is well known that silicon highly doped withboron is an effective etch stop in silicon anisotropic etches (i.e.,KOH, EDP, TMAH). By intensely boron doping the tip, the body of the tipcan be etched away from the back side, leaving only the outside shell ofthe tip. This is advantageous because it will reduce the mass of the tipwithout affecting its functionality. Operationally, the benefit of alower mass tip is that it will cause the resonant frequency of thedevice to increase. Higher resonant frequency cantilevers, with similarspring constants, have been shown to provide higher resolutions andfaster responses when used as sensors.

Turning to FIG. 1B, a silicon dioxide (SiO₂) layer 66, is grown over thewafer including the silicon stylus 60. This layer is grown inconventional fashion in a manner that will cause the silicon tip tobecome sharper. An example of this would be an oxidation step usingsteam at 950 degrees C., a well known process. The thickness of theresulting oxide layer should be great enough to serve as an etch stopfor the subsequent silicon nitride etch. Typically, 0.25 nm is apreferred thickness for the oxide layer. A silicon nitride layer 68 isthen deposited over the silicon dioxide layer 66. The silicon nitridelayer 68 is deposited by one of a group including chemical vapordeposition (CVD), low pressure chemical vapor deposition (LPCVD), plasmaenhanced chemical vapor deposition, chemical deposition, evaporation andsputtering, and is preferably 10 nm to 10 μm thick.

As will become apparent, it is the oxide layer 66 that operates not onlyas an etch stop but as an intermediate “bonding” layer between thesilicon tip and the silicon nitride cantilever.

A protective coating 70 is then deposited on the silicon nitride layer68. Preferably, coating 70 is a photoresist applied by spin coating, sothat the coating thickness is less than the height of the siliconnitride covered silicon stylus 60. An additional lithography step, whichclears any resist from the apex 62 of tip 60, could be used at thispoint.

More particularly, the height of the tip 60 is known from priorprocessing. And, the properties of the resist are typically well knownby the manufacturer, with the resist typically being provided with alook-up table that contains values for the final resist thickness fordifferent spin speeds and durations. Notably, even though the apexes ofthe tips may be covered by the initial application of the resist, thesubsequent spin planarazation will clear them adequately. If this is aconcern, a quick resist etch may be applied to clear any residual resist“scum” from the apex 62. This process will leave a very thin coating, tono coating, of resist on the apex of the stylus.

Turning to FIG. 1C, a silicon nitride covered silicon stylus 60 isetched to expose the underlying silicon dioxide layer 66, but notover-etched to the point that the silicon stylus 60 is exposed. The etchcontrol is accomplished by knowing the etch rates of both the film beingetched, the etch stop, and the etch mask of the particular etch toolbeing used. With these numbers, along with knowledge of the thickness ofthe film being etched, the etch stop, and the etch mask, a processwindow can be calculated that will give a range of etch times that willclear the stylus without clearing the etch stop or the etch mask. Ifthese calculations do not yield an adequate etch window, the etchprocess or etch tool must be changed to increase the selectivity of theetch to the etch stop and the etch mask. This protects the apex 62 ofthe stylus 60 from this etch, and the subsequent cantilever releaseetch. In many cases, the combination of the etch selectivity betweensilicon nitride 68 and the resist 70, and the height of the siliconnitride coated stylus will require multiple coatings of resist 70 to beapplied. This would occur if all the resist is etched off the waferbefore the silicon nitride on the silicon stylus is completely removed.The old resist can optionally be stripped off and new resist applied,and the etch continued.

Notably, during the clearing of the apex it is often convenient topattern the shape of the cantilever. This is done by standardphotolithography either during the stylus clearing or in a subsequentlithography step. It should be noted that photoresist need only be usedif lithography is employed. Otherwise polyimides, epoxies, waxes, etc.can be used for the tip definition. Also, consumption of resist by theetch can be used, in conjunction with the total resist thickness, totailor the amount of the stylus 60 that will be exposed. After thestylus has been exposed by the etch, the remaining resist is removedfrom the top silicon working surface of the wafer in conventionalfashion.

Turning to FIG. 1D, a device is now released by etching away the backside silicon. This etch is stopped when the silicon is removed fromunder the silicon nitride layer 68 (i.e., cantilever), but before thesilicon stylus 60 is removed. In the case of an SOI wafer, the middleoxide is used as an etch stop.

The silicon dioxide layer 66 may then be removed. The protective oxidelayer is preferably removed in an etch that is highly selective tosilicon nitride and silicon, such as 6:1 buffered oxide etch, so thatthe characteristics of the tip (for example, sharpness) are notcompromised.

As a result, the silicon dioxide is removed without unbonding thesilicon tip 60 from the silicon nitride cantilever. In sum, an oxidelayer 66 is inserted so that the tip 1) is protected to the end of theprocess (i.e., the oxide operates as a passivating layer), and 2) iscoupled to the silicon nitride, albeit via the oxide. In the completeddevice, the tip 60 is cleared of oxide on its apex, but again not in theregion that affixes the tip 60 to the silicon nitride 68. Therefore, themethod removes the silicon nitride from the tip 60 while at the sametime preserves the designed characteristics of the tip. Notably, becausethe oxide passivation layer protects the tip throughout the entireprocess, including the exposing of the apex, but also through therelease of the cantilever structure, the step of releasing thecantilever 68 via the backside silicon wafer etch does not ruin the tip60.

A reflective coating 72 may then be deposited on a back side 74 of thecantilever 68. Again, this coating 72 may serve multiple purposesincluding, for example, a surface for reflecting a laser beam toward aphotodetector in an optical beam-bounce measurement apparatus. Thereflective coating can optionally be applied, in process, on the frontside of the cantilever. This is advantageous because the reflectivecoating can be patterned into a specific shape. An example of a usefulshape would be a reflective coating near the free end of the cantileverbut not on the base of the cantilever. This configuration also wouldminimize the residual bending of the cantilever due to stress in theapplied reflective film, and bending from thermal effects.

FIGS. 2A-2D illustrate steps for making a silicon nitride layer with aprotruding silicon stylus and a front side reflective coating. Theprocess is the same as with respect to FIGS. 1A-1D, only now areflective film 80 is deposited over the silicon nitride 68. This film80 may or may not be patterned separately from patterning the cantileverstructure. The film is patterned separately when the desired shape ofthe reflector is different from the desired shape of the cantilever.This may be done to optimize cantilever parameters such as stress orreflectivity. If patterned separately, it is removed from the stylusstack before the silicon nitride stylus clearing etch. If a separatelithography is not used, this reflective coating can be cleared in thesame manner as the silicon nitride 68, only with a suitable etch. Anadditional lithography, which clears the resist 70 from the apex 62 ofthe tip 60, could be used at this point.

Notably, the process illustrated in FIGS. 2A-2D is contrary toconventional practice in, for example, producing probes for surfaceanalysis tools such as an atomic force microscope. Again, inconventional production, the metal reflector is disposed on the backside of the cantilever in the final step of production because the laserused in the measurement apparatus (e.g., using an optical beam-bouncetechnique) is typically reflected off the back side of the cantilever.And, in conventional production, the last step is the first time theback side of the cantilever is revealed so it cannot be depositedearlier in the process.

The result of the process illustrated in FIG. 2D is a reflector on thefront side of the cantilever, disposed in process prior to the back sidebeing revealed. Because the cantilever is transparent, a suitablereflector results, much how the metalization on a household mirror isdisposed on the far side of the glass.

This technique has significant advantages including the fact that themetal reflector can be shaped, and thus can be kept separate fromcritical elements. Moreover, it is easier to process and more robust,and stress can be better controlled because the substrate is morestable. And, the process yields less worry about residual coating of thetip 60 because the reflective film 80 is actively etched away.

Moreover, this technique is particularly useful when producing thincantilevers that need reflectors. The AFM industry, for one, seems to bemoving towards thinner levers, and therefore thinners reflectors. Thisprocess of producing a front side reflector can offer improvements overbulk back side coating because, as noted above, by patterning thereflector just where you need it, you can eliminate stress problems andthermal drift problems.

FIGS. 3A-3D illustrate the fundamental steps for making a siliconnitride layer with a protruding metal stylus 90. The same process isused as in forming the silicon stylus (FIGS. 1A-1D), only the etch isnot stopped when the field silicon is clear, but when all the silicon isconsumed, as shown in FIG. 3C. If an SOI wafer is used, an extra oxideetch must be inserted, as appreciated by those skilled in the art. Ametal film 90 is then deposited from the back side of the cantileveruntil the hole or aperture 92 formed by the removed silicon stylus isfilled with metal and metal protrudes beyond silicon nitride cantileverto define stylus or tip 90. The result of the deposition will be theformation of a metal tip 90 with electrical contact to the base of thecantilever. Notably, the metal tip will be self-sharpening to a degree.As the aperture closes the apex will come to a point. However, ittypically is not nearly as sharp as the silicon tip. This is acceptableas “metal tip” applications usually do not require a tip as sharp asapplications that require a silicon tip.

FIGS. 4A and 4B illustrate the fundamental steps for making a siliconnitride layer with a protruding thermally sensitive stylus. Thestructure of FIGS. 3A to 3D is formed and therefore the previous stepswill not be repeated. Thereafter, a dissimilar metal 100 is thendeposited on the front or top surface 102 of the cantilever. Thejunction of the two metals 90, 100, which only occurs substantially atthe apex 110 of tip 108, forms a thermocouple. As previously noted, itis well known that dissimilar metals in contact will produce a voltagethat is proportional to temperature. Electrical contact is made to thethermocouple from contacting the respective metals 90, 100 on themounting section area 104, 106, respectively.

Turning to FIG. 5, a method 110 of producing a silicon nitridecantilever having a silicon tip is shown. Initially, in Block 112, asubstrate, such as a silicon wafer or a silicon-on-insulator wafer, isprovided. Then, one or more tips or styluses are formed on the workingsurface of the substrate in Block 114. At this point, an optional dopingstep may be performed to alter the make-up of the silicon stylus(es) inBlock 116, as described previously. Again, this doping step may beperformed to alter electrical properties of the tip, or to form a“shell” tip, etc.

Next, in Block 118, an oxide layer is deposited on the top workingsurface of the substrate. Preferably, this oxide layer acts as asharpening step that results in a silicon dioxide layer residing on thesilicon substrate including the silicon tips. Then, a cantilevermaterial layer (preferably, silicon nitride) is deposited on the silicondioxide layer in Block 120. Once the silicon nitride layer is formed soas to provide a cantilever having a selected thickness, a protectivecoating is deposited on the top working surface in Block 122.Preferably, this is a spin coated resist that is deposited inconventional fashion.

In Block 124, the apex of the tip is cleared of the silicon nitride.This is accomplished by using an appropriate etch. Notably, the shape ofthe cantilever can be patterned in an optional operation as part ofBlock 124.

Importantly, upon completion of clearing the apex in Block 124, theprotective silicon dioxide layer remains on the tip. In Block 126, thecantilever is released by etching away the silicon from the back side ofthe wafer. Notably, the integrity of the characteristics of the tip aremaintained in this step due to the fact that the silicon dioxide layerremains on the tip.

Once the cantilever is released in Block 126, the silicon dioxide on thetip (and back side of substrate) is removed using an appropriate etch soas to not compromise the integrity (e.g., sharpness) of the tip in Block128. Then, in Block 130, a reflective coating is deposited on thecantilever of the probe from the back side working surface. Of course,as highlighted above in discussing FIGS. 2A-2D, this reflective coatingmay be deposited on the front side working surface of the wafer duringformation of the cantilever, after deposition of the silicon nitridelayer in Block 120. Method 110 is terminated in Block 132, to produce ascanning probe device suitable for use in, for example, an atomic forcemicroscope.

Although the best mode contemplated by the inventors of carrying out thepresent invention is disclosed above, practice of the present inventionis not limited thereto. It will be manifest that various additions,modifications and rearrangements of the features of the presentinvention may be made without deviating from the spirit and scope of theunderlying inventive concept. The scope of still other changes to thedescribed embodiments that fall within the present invention but thatare not specifically discussed above will become apparent from theappended claims.

1. A method of making a probe having a cantilever and a tip, the methodcomprising the steps of: providing a substrate having a surface, the tipextending from the surface; depositing an etch stop on the substrate,the etch stop protecting the tip; depositing a cantilever material layeron the etch stop to form the cantilever; and performing an etchoperation of the cantilever material to expose the etch stop protectingthe tip; and removing part of the etch stop from the tip to expose thetip, wherein another part of the etch stop is maintained between thecantilever and the tip.
 2. The method of claim 1, further comprisingreleasing the cantilever material layer to form the cantilever, thecantilever having a front side and a back side.
 3. The method of claim2, wherein said releasing step includes etching the substrate.
 4. Themethod of claim 3, wherein the substrate is a silicon wafer, and saidetching step includes not removing the tip silicon.
 5. The method ofclaim 3, wherein the substrate is a silicon wafer, and wherein saidetching step includes removing the tip silicon.
 6. The method of claim5, further comprising the step of depositing a first metal from the backside of the cantilever so as to form a metal tip.
 7. The method of claim6, further comprising depositing a second metal from the front sidetowards the cantilever so as to create a junction of the first andsecond metals at an apex of the metal tip.
 8. The method of claim 2,further comprising removing the etch stop from the tip.
 9. The method ofclaim 8, wherein said removing step includes using an oxide etch. 10.The method of claim 8, further comprising applying a reflective coatingto the back side.
 11. The method of claim 1, wherein said depositing anetch stop step sharpens the tip.
 12. The method of claim 11, wherein theetch stop is silicon dioxide.
 13. The method of claim 12, wherein theetch stop is less than about 0.30 nm.
 14. The method of claim 1, furthercomprising the step of doping the tip.
 15. The method of claim 14,wherein said doping step is performed prior to said depositing the etchstop step.
 16. The method of claim 1, further comprising depositing areflective coating on the cantilever material layer.
 17. The method ofclaim 1, wherein said depositing the cantilever material layer isperformed using CVD.
 18. The method of claim 1, wherein the cantilevermaterial layer is silicon nitride.
 19. The method of claim 1, furthercomprising exposing the tip using multiple applications of an etch mask.20. The method of claim 1, further comprising shaping the cantilever.21. The method of claim 20, wherein both said exposing the tip and saidshaping the cantilever steps are performed using the etch mask.
 22. Themethod of claim 1, wherein the probe has a front side and a back side,and wherein the probe is electrically accessed through both sides.
 23. Amethod of making a probe comprising the steps of: providing a waferincluding silicon; forming a stylus on a surface of the wafer; oxidizingthe silicon; depositing a silicon nitride layer to form a cantilever ofthe probe; and revealing the stylus using a subsequent etch, wherein theetch is terminated on at least part of the stylus, wherein the oxidizedsilicon is substantially removed from the apex of the stylus but ismaintained between the cantilever and the stylus.
 24. The method ofclaim 23, further comprising releasing the silicon nitride layer to forma cantilever having a back side.
 25. The method of claim 24, furthercomprising applying a reflective coating to the back side.
 26. Themethod of claim 23, wherein a reflective coating is formed prior to saiddepositing a silicon nitride layer step.
 27. The method of claim 23,wherein said oxidizing step includes thermally growing an oxide tosharpen and protect the stylus.
 28. The method of claim 27, wherein theoxide is silicon dioxide.